Undefined Behavior in GCC 4.8 ios_base.h

Bug #1514309 reported by Jeffrey Walton on 2015-11-09
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Fix Released
gcc-4.8 (Ubuntu)
gcc-5 (Debian)
Fix Released
gcc-5 (Ubuntu)

Bug Description

On Linux, the distros often use libstdc++ rather than libc++ for Clang. Building libcxx is an art that I have never been able to untangle, and I think the maintainers have discovered the same.

Below, I'm catching a UB finding when using Clang and libstdc++. This one has been around for some time. I first encountered it on Apple platforms. I regularly encounter it on Debian and Ubuntu.

The fix is fairly easy, and I usually just do it: a couple of casts among unsigned and the flags. Also see http://lists.llvm.org/pipermail/cfe-dev/2015-January/040753.html.


$ cat ub.cxx
#include <iostream>

int main(int argc, char* argv[])
  std::cout << std::hex << argc << std::endl;
  std::cout << std::dec << argc << std::endl;
  return 0;

$ clang++ -fsanitize=undefined ub.cxx -o ub.exe

$ ./ub.exe
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/ios_base.h:96:24: runtime error: load of value 4294967221, which is not a valid value for type 'std::_Ios_Fmtflags'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/ios_base.h:76:67: runtime error: load of value 4294967221, which is not a valid value for type 'std::_Ios_Fmtflags'


$ g++ --version
g++ (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4

$ uname -a
Linux ubuntu 3.13.0-66-generic #108-Ubuntu SMP Wed Oct 7 15:20:27 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release
No LSB modules are available.


$ apt-cache show g++
Package: g++
Priority: optional
Section: devel
Installed-Size: 34
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: Debian GCC Maintainers <email address hidden>
Architecture: amd64
Source: gcc-defaults (1.124ubuntu6)
Version: 4:4.8.2-1ubuntu6
Provides: c++-compiler
Depends: cpp (>= 4:4.8.2-1ubuntu6), gcc (>= 4:4.8.2-1ubuntu6), g++-4.8 (>= 4.8.2-5~), gcc-4.8 (>= 4.8.2-5~)
Suggests: g++-multilib
Filename: pool/main/g/gcc-defaults/g++_4.8.2-1ubuntu6_amd64.deb
Size: 1490
MD5sum: 7332a4e9116b821e167a3d0236ca413a
SHA1: 2c7201808be1029d21b7691c5a855535a4fcbd51
SHA256: 02c3d204efe6c34bf3de655aaf6a9ce524511977aedf92d7bce7093d0581f977
Description-en: GNU C++ compiler
 This is the GNU C++ compiler, a fairly portable optimizing compiler for C++.
 This is a dependency package providing the default GNU C++ compiler.
Description-md5: 4d44b18774ae5123b7c3f70d940cf655
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Build-Essential: yes
Origin: Ubuntu
Supported: 5y

Matthias Klose (doko) on 2015-11-18
affects: gcc-defaults (Ubuntu) → gcc-4.8 (Ubuntu)
Changed in gcc-4.8 (Ubuntu):
status: New → Confirmed
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package gcc-4.8 - 4.8.5-2ubuntu1

gcc-4.8 (4.8.5-2ubuntu1) xenial; urgency=medium

  * Merge with Debian; remaining changes:
    - Build from the upstream source.

gcc-4.8 (4.8.5-2) unstable; urgency=medium

  * Update the Linaro support to the 4.8-2015.07 release.
  * Adjust setting DH_COMPAT for dh_movefiles with updated debhelper supporting
    globbing of arguments. Closes: #800248.
  * Fix PR libstdc++/56158, taken from the trunk.
    Addresses: #804521. LP: #1514309.
  * Backport fixes to allow building with cloog-0.18.4 and isl-0.15.
  * Backport PR target/67281 from the trunk (HTM fixes). LP: #1517093.
  * Fix auto-loading of gdb pretty printers. LP: #1446828.

 -- Matthias Klose <email address hidden> Wed, 18 Nov 2015 19:57:42 +0100

Changed in gcc-4.8 (Ubuntu):
status: Confirmed → Fix Released

Hello Jeffrey, or anyone else affected,

Accepted gcc-4.8 into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gcc-4.8/4.8.4-2ubuntu1~14.04.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in gcc-4.8 (Ubuntu Trusty):
status: New → Fix Committed
tags: added: verification-needed
Changed in gcc-4.8 (Ubuntu):
importance: Undecided → Medium
Changed in gcc-4.8 (Ubuntu Trusty):
importance: Undecided → Medium
Mathew Hodson (mathew-hodson) wrote :
no longer affects: gcc-5 (Ubuntu Trusty)
Changed in gcc-5 (Ubuntu):
importance: Undecided → Medium
status: New → Fix Released
Changed in gcc-5 (Debian):
status: Unknown → Fix Released
Matthias Klose (doko) wrote :

verified that the proposed libstdc++-4.8-dev, when used with clang, doesn't show this runtime error.

tags: added: verification-done
removed: verification-needed
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package gcc-4.8 - 4.8.4-2ubuntu1~14.04.1

gcc-4.8 (4.8.4-2ubuntu1~14.04.1) trusty-proposed; urgency=medium

  * SRU:
  * Fix auto-loading of gdb pretty printers. LP: #1446828.
  * Fix PR libstdc++/56158, taken from the trunk.
    Addresses: #804521. LP: #1514309.
  * Backport PR target/64579 and PR target/67281 from the trunk (HTM fixes).
    LP: #1517093.

 -- Matthias Klose <email address hidden> Wed, 18 Nov 2015 17:48:36 +0100

Changed in gcc-4.8 (Ubuntu Trusty):
status: Fix Committed → Fix Released

The verification of the Stable Release Update for gcc-4.8 has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

Changed in gcc:
importance: Unknown → Medium
status: Unknown → Fix Released
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